package com.wkcto.threadlocal;

/**
 * ThreadLocal的基本使用
 */
public class Test01 {
    //定義ThreadLocal對象
    static  ThreadLocal threadLocal = new ThreadLocal();
    //定義線程類
    static  class  Subthread extends Thread{
        @Override
        public void run() {
            for (int i = 0; i < 20; i++) {
                //設置線程關聯的的值
                threadLocal.set( Thread.currentThread().getName() + " - " + i);
                //調用get()方法讀取關聯的值
                System.out.println(Thread.currentThread().getName() + " value = " + threadLocal.get());
            }
        }
    }

    public static void main(String[] args) {
        Subthread t1 = new Subthread();
        Subthread t2 = new Subthread();
        t1.start();
        t2.start();

    }
}

package com.wkcto.threadlocal;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

/**
 *  在多線程環境中,把字符串轉換為日期對象,多個線程使用同一個SimpleDateFormat對象可能會產生線程安全問題,有異常
 *  為每個線程指定自己的SimpleDateFormat對象, 使用ThreadLocal
 */
public class Test02 {
    //定義SimpleDateFormat對象,該對象可以把字符串轉換為日期
//    private static SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");
    static ThreadLocal threadLocal = new ThreadLocal<>();
    //定義Runnable接口的實現類
    static class ParseDate implements Runnable{
        private  int i = 0 ;
        public ParseDate(int i) {
            this.i = i;
        }

        @Override
        public void run() {
            try {
                String text = "2068年11月22日 08:28:" + i%60;      //構建日期字符串
//                Date date = sdf.parse(text);        //把字符串轉換為日期
                //先判斷當前線程是否有SimpleDateFormat對象,如果當前線程沒有SimpleDateFormat對象就創建一個,如果有就直接使用
                if (threadLocal.get() == null){
                    threadLocal.set(new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss"));
                }
                Date date = threadLocal.get().parse(text);
                System.out.println(i + " -- " + date);
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        //創建100個線程
        for (int i = 0; i < 100; i++) {
            new Thread(new ParseDate(i)).start();
        }
    }
}

package com.wkcto.threadlocal;

import java.util.Date;
import java.util.Random;

/**
 * ThreadLocal初始值, 定義ThreadLocal類的子類,在子類中重寫initialValue()方法指定初始值,再第一次調用get()方法不會返回null
 */
public class Test03 {
    //1) 定義ThreadLocal的子類
    static class SubThreadLocal extends ThreadLocal{
        // 重寫initialValue方法,設置初始值
        @Override
        protected Date initialValue() {
//            return new Date();  //把當前日期設置為初始化
            return  new Date(System.currentTimeMillis() - 1000*60*15);
        }
    }

    //定義ThreadLocal對象
//    static ThreadLocal threadLocal = new ThreadLocal();
    //直接使用自定義的SubThreadLocal對象
    static SubThreadLocal threadLocal = new SubThreadLocal();

    //定義線程類
    static class SubThread extends  Thread{
        @Override
        public void run() {
            for (int i = 0; i < 10; i++) {
                //第一次調用threadLocal的get()方法會返回null
                System.out.println("---------" + Thread.currentThread().getName() + " value=" + threadLocal
                .get());
                //如果沒有初始值就設置當前日期
                if ( threadLocal.get() == null ){
                    System.out.println("*****************");
                    threadLocal.set(new Date());
                }
                try {
                    Thread.sleep(new Random().nextInt(500));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        SubThread t1 = new SubThread();
        t1.start();
        SubThread t2 = new SubThread();
        t2.start();
    }
}